1. Field of the Invention
The present invention pertains to narrowband telephony and data communications, and particularly to using a broadband transport for narrowband telephony and data communications.
2. Related Art and Other Considerations
The increasing interest for high band services such as multimedia applications, video on demand, video telephone, and teleconferencing has motivated development of the Broadband Integrated Service Digital Network (B-ISDN). B-ISDN is based on a technology know as Asynchronous Transfer Mode (ATM), and offers considerable extension of telecommunications capabilities.
ATM is a packet-oriented transfer mode which uses asynchronous time division multiplexing techniques. Packets are called cells and traditionally have a fixed size. A traditional ATM cell comprises 53 octets, five of which form a header and forty eight of which constitute a “payload” or information portion of the cell. The header of the ATM cell includes two quantities which are used to identify a connection in an ATM network over which the cell is to travel, particularly the VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). In general, the virtual is a principal path defined between two switching nodes of the network; the virtual channel is one specific connection on the respective principal path.
At its termination points, an ATM network is connected to terminal equipment, e.g., ATM network users. Typically between ATM network termination points there are plural switching nodes, the switching nodes having ports which are connected together by physical transmission paths or links. Thus, in traveling from an originating terminal equipment to a destination terminal equipment, ATM cells forming a message may travel through several switching nodes.
A switching node has a plurality of ports, each of which can be connected by via a link circuit and a link to another node. The link circuit performs packaging of the cells according to the particular protocol in use on the link. A cell incoming to a switching node may enter the switching node at a first port and exit from a second port via a link circuit onto a link connected to another node. Each link can carry cells for plural connections, a connection being e.g., a transmission between a calling subscriber or party and a called subscriber or party.
The switching nodes each typically have several functional parts, a primary of which is a switch core. The switch core essentially functions like a cross-connect between ports of the switch. Paths internal to the switch core are selectively controlled so that particular ports of the switch are connected together to allow a message ultimately to travel from an ingress side of the switch to an egress side of the switch, and ultimately from the originating terminal equipment to the destination terminal equipment.
While ATM is envisioned as the transport mechanism for more advanced services such as Broadband ISDN (B-ISDN), it nevertheless must be recognized that the current narrow band networks (e.g., PSTN, ISDN) will remain (at least in part) for quite some time. It has taken decades for the present voice switched telephony networks (e.g., PSTN, ISDN) to reach their present advanced functionalities. While ATM networks are being built, the ATM networks likely will not easily acquire all the functionalities of advanced voice communication. Therefore, at least initially, ATM will in some instances be added to or replace parts of a circuit switched telephony network. In such instances ATM will be used for transport and switching.
U.S. Pat. Nos. 5,568,475 and 5,483,527 to Doshi et al. incorporate ATM switches for routing telephony voice signals between Synchronous Transfer Mode (STM) nodes. The ATM switches use a signaling system No. 7 (SS#7) network to establish a virtual connection, rather than a circuit switched connection (as would be the case in pure STN network). The signaling system No. 7 (SS#7) network of U.S. Pat. Nos. 5,568,475 and 5,483,527 includes signal transfer points (STPs) which are connected by special physical links to each of the ATM switch nodes. For call setup, for example, signaling messages are relayed through the non-ATM signaling system No. 7 network. In such relaying, a non-ATM STP receives the signaling message and advises its associated ATM node of the call setup. The associated ATM node then can identify idle resources to be used for forwarding voice signals to the next ATM node once the call has been setup, and prepares its own signaling message to be used in the relay. The signaling message prepared by the ATM node is returned to its associated STP, which forwards the signaling message via the signaling system No. 7 network to another STP associated with the next ATM node. Such relaying continues until the signaling message reaches a STP of a STM local exchange carrier-(LEC). Once the call has been set up, the ensuing speech (or voice-band data) is transported via the ATM nodes. STM/ATM terminal adapters are situated between the STM network and the ATM network for packing samples of voice signals as received from the STM network into ATM cells for application to the ATM network, and for unpacking ATM cell payloads to obtain voice signals for application to the STM network.
The incorporation of ATM into an STM network in the particular manner as descried above thus involves a non-ATM signaling network alongside the ATM nodes. What is needed therefore, and an object of the present invention, is a grafting of a network of ATM switches into an STM network in a manner whereby a separate physical signaling interface is not required for signaling purposes.